Difference between revisions of "2014 AMC 12B Problems/Problem 21"
(→Solution 4) |
(→Solution 4) |
||
Line 69: | Line 69: | ||
− | + | <cmath>a + sin(k) \cdot 1 + cos(k)a = 1</cmath> | |
− | < | + | <cmath>sin(k)a + cos(k) = 1</cmath> |
Solving for <math>a</math> we get: | Solving for <math>a</math> we get: | ||
− | + | <cmath>a = \frac{1-sin(k)}{cos(k) + 1} = \frac{1 - cos(k)}{sin(k)}</cmath> | |
<math>(1-sin(k)) \cdot sin(k) = (1 - cos(k))\cdot(cos(k) + 1)</math> | <math>(1-sin(k)) \cdot sin(k) = (1 - cos(k))\cdot(cos(k) + 1)</math> |
Revision as of 10:58, 29 November 2016
Problem 21
In the figure, is a square of side length . The rectangles and are congruent. What is ?
Solution 1
Draw the altitude from to and call the foot . Then . Consider . It is the hypotenuse of both right triangles and , and we know , so we must have by Hypotenuse-Leg congruence. From this congruence we have .
Notice that all four triangles in this picture are similar. Also, we have . So set and . Now . This means , so is the midpoint of . So , along with all other similar triangles in the picture, is a 30-60-90 triangle, and we have and subsequently . This means , which gives , so the answer is .
Solution 2
Let . Let . Because and , are all similar. Using proportions and the pythagorean theorem, we find Because we know that , we can set up a systems of equations Solving for in the second equation, we get Plugging this into the first equation, we get Plugging into the previous equation with , we get
Solution 3
Let , , and . Then and because and , . Furthermore, the area of the four triangles and the two rectangles sums to 1:
By the Pythagorean theorem:
Then by the rational root theorem, this has roots , , and . The first and last roots are extraneous because they imply and , respectively, thus .
Solution 4
Let = and = . It is shown that all four triangles in the picture are similar. From the square side lengths:
Solving for we get:
[/center]
See also
2014 AMC 12B (Problems • Answer Key • Resources) | |
Preceded by Problem 20 |
Followed by Problem 22 |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | |
All AMC 12 Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.